The present invention concerns an electronic switching ballast circuit, wherein a part of the load supplying output voltage is fed back to arbitrarily limit the pulse width so as to modify the output into a sine wave.
Conventionally, a fluorescent lamp is lighted by using a choke transformer to cause a magnetic cathode preheating discharge. The drawbacks to this conventional method are that more than five seconds are needed for the lighting time, and a low frequency voltage of about 50 to 60 Hz resulting in faltering light is used, causing viewing problems and making it impossible to use this method at low voltages and low temperatures. Moreover, this conventional method results in frequency interferences with other electronic appliances, is likely to cause fire damage due to overload, and decreases durability of the lamp.
Recently, a low frequency oscillating electronic ballast using a choke transformer has been developed. Although this makes it possible to light the lamp instantly, the choke transformer consumes a large amount of power and uses low frequency causing the viewing problems due to faltering light.